diff --git a/pandas/io/common.py b/pandas/io/common.py
index f9cd1806763e2..79c4f1ca4f83c 100644
--- a/pandas/io/common.py
+++ b/pandas/io/common.py
@@ -9,12 +9,14 @@
 import lzma
 import mmap
 import os
+import pathlib
 from urllib.error import URLError  # noqa
 from urllib.parse import (  # noqa
     urlencode, urljoin, urlparse as parse_url, uses_netloc, uses_params,
     uses_relative)
 from urllib.request import pathname2url, urlopen
 import zipfile
+from typing import AnyStr, IO, Union
 
 from pandas.errors import (  # noqa
     AbstractMethodError, DtypeWarning, EmptyDataError, ParserError,
@@ -22,6 +24,8 @@
 
 from pandas.core.dtypes.common import is_file_like
 
+from pandas._typing import FilePathOrBuffer
+
 # gh-12665: Alias for now and remove later.
 CParserError = ParserError
 
@@ -67,7 +71,8 @@ def _is_url(url):
         return False
 
 
-def _expand_user(filepath_or_buffer):
+def _expand_user(
+        filepath_or_buffer: FilePathOrBuffer) -> FilePathOrBuffer:
     """Return the argument with an initial component of ~ or ~user
        replaced by that user's home directory.
 
@@ -82,6 +87,8 @@ def _expand_user(filepath_or_buffer):
     """
     if isinstance(filepath_or_buffer, str):
         return os.path.expanduser(filepath_or_buffer)
+    elif isinstance(filepath_or_buffer, pathlib.Path):
+        return filepath_or_buffer.expanduser()
     return filepath_or_buffer
 
 
@@ -93,7 +100,8 @@ def _validate_header_arg(header):
                         "the row(s) making up the column names")
 
 
-def _stringify_path(filepath_or_buffer):
+def _stringify_path(
+        filepath_or_buffer: FilePathOrBuffer) -> Union[str, IO[AnyStr]]:
     """Attempt to convert a path-like object to a string.
 
     Parameters
@@ -115,12 +123,6 @@ def _stringify_path(filepath_or_buffer):
     Any other object is passed through unchanged, which includes bytes,
     strings, buffers, or anything else that's not even path-like.
     """
-    try:
-        import pathlib
-        _PATHLIB_INSTALLED = True
-    except ImportError:
-        _PATHLIB_INSTALLED = False
-
     try:
         from py.path import local as LocalPath
         _PY_PATH_INSTALLED = True
@@ -128,12 +130,17 @@ def _stringify_path(filepath_or_buffer):
         _PY_PATH_INSTALLED = False
 
     if hasattr(filepath_or_buffer, '__fspath__'):
-        return filepath_or_buffer.__fspath__()
-    if _PATHLIB_INSTALLED and isinstance(filepath_or_buffer, pathlib.Path):
-        return str(filepath_or_buffer)
+        # mypy lacks comprehensive support for hasattr; see mypy#1424
+        # TODO (PY36): refactor to use os.PathLike
+        return filepath_or_buffer.__fspath__()  # type: ignore
     if _PY_PATH_INSTALLED and isinstance(filepath_or_buffer, LocalPath):
         return filepath_or_buffer.strpath
-    return _expand_user(filepath_or_buffer)
+
+    expanded = _expand_user(filepath_or_buffer)
+    if isinstance(expanded, pathlib.Path):
+        return str(expanded)
+
+    return expanded
 
 
 def is_s3_url(url):
diff --git a/pandas/io/json/json.py b/pandas/io/json/json.py
index ee9d9e000d7e3..88fc08a447d2c 100644
--- a/pandas/io/json/json.py
+++ b/pandas/io/json/json.py
@@ -1,6 +1,7 @@
 from io import StringIO
 from itertools import islice
 import os
+from typing import Callable, Optional, Type, Union
 
 import numpy as np
 
@@ -12,6 +13,7 @@
 from pandas.core.dtypes.common import is_period_dtype
 
 from pandas import DataFrame, MultiIndex, Series, isna, to_datetime
+from pandas._typing import FilePathOrBuffer
 from pandas.core.reshape.concat import concat
 
 from pandas.io.common import (
@@ -30,16 +32,24 @@
 
 
 # interface to/from
-def to_json(path_or_buf, obj, orient=None, date_format='epoch',
-            double_precision=10, force_ascii=True, date_unit='ms',
-            default_handler=None, lines=False, compression='infer',
-            index=True):
+def to_json(
+        path_or_buf: FilePathOrBuffer,
+        obj: Union[Series, DataFrame],
+        orient: str = None,
+        date_format: str = 'epoch',
+        double_precision: int = 10,
+        force_ascii: bool = True,
+        date_unit: str = 'ms',
+        default_handler: Callable = None,
+        lines: bool = False,
+        compression: str = 'infer',
+        index: bool = True) -> Optional[str]:
 
     if not index and orient not in ['split', 'table']:
         raise ValueError("'index=False' is only valid when 'orient' is "
                          "'split' or 'table'")
 
-    path_or_buf = _stringify_path(path_or_buf)
+    str_or_io = _stringify_path(path_or_buf)
     if lines and orient != 'records':
         raise ValueError(
             "'lines' keyword only valid when 'orient' is records")
@@ -47,7 +57,7 @@ def to_json(path_or_buf, obj, orient=None, date_format='epoch',
     if orient == 'table' and isinstance(obj, Series):
         obj = obj.to_frame(name=obj.name or 'values')
     if orient == 'table' and isinstance(obj, DataFrame):
-        writer = JSONTableWriter
+        writer = JSONTableWriter  # type: Type[Writer]
     elif isinstance(obj, Series):
         writer = SeriesWriter
     elif isinstance(obj, DataFrame):
@@ -64,16 +74,19 @@ def to_json(path_or_buf, obj, orient=None, date_format='epoch',
     if lines:
         s = _convert_to_line_delimits(s)
 
-    if isinstance(path_or_buf, str):
-        fh, handles = _get_handle(path_or_buf, 'w', compression=compression)
+    if isinstance(str_or_io, str):
+        fh, handles = _get_handle(
+            str_or_io, 'w', compression=compression)
         try:
             fh.write(s)
         finally:
             fh.close()
-    elif path_or_buf is None:
+    elif str_or_io is None:
         return s
     else:
-        path_or_buf.write(s)
+        str_or_io.write(s)
+
+    return None
 
 
 class Writer: