where does access point's IP address come from for sketch AP_SimpleWebServer.ino in Github WiFi101 examples
If you look into that github source code, you can see startAP function and mainly rows with strM2MAPConfig.au8DHCPServerIP:

uint8_t WiFiClass::startAP(const char *ssid, uint8_t u8SecType, const void *pvAuthInfo, uint8_t channel)
{
    tstrM2MAPConfig strM2MAPConfig;

    if (!_init) {
        init();
    }

    if (channel == 0) {
        channel = 1; // channel 1 is the minium channel
    }

    // Enter Access Point mode:
    memset(&amp;strM2MAPConfig, 0x00, sizeof(tstrM2MAPConfig));
    strcpy((char *)&amp;strM2MAPConfig.au8SSID, ssid);
    strM2MAPConfig.u8ListenChannel = channel - 1;
    strM2MAPConfig.u8SecType = u8SecType;
    strM2MAPConfig.au8DHCPServerIP[0] = 0xC0; /* 192 */
    strM2MAPConfig.au8DHCPServerIP[1] = 0xA8; /* 168 */
    strM2MAPConfig.au8DHCPServerIP[2] = 0x01; /* 1 */
    strM2MAPConfig.au8DHCPServerIP[3] = 0x01; /* 1 */

    if (u8SecType == M2M_WIFI_SEC_WEP) {
        tstrM2mWifiWepParams* wep_params = (tstrM2mWifiWepParams*)pvAuthInfo;

        strM2MAPConfig.u8KeyIndx = wep_params-&gt;u8KeyIndx;
        strM2MAPConfig.u8KeySz = wep_params-&gt;u8KeySz;
        strcpy((char*)strM2MAPConfig.au8WepKey, (char *)wep_params-&gt;au8WepKey);
    }

    if (m2m_wifi_enable_ap(&amp;strM2MAPConfig) &lt; 0) {
        _status = WL_CONNECT_FAILED;
        return _status;
    }
    _status = WL_AP_LISTENING;
    _mode = WL_AP_MODE;

    memset(_ssid, 0, M2M_MAX_SSID_LEN);
    memcpy(_ssid, ssid, strlen(ssid));
    m2m_memcpy((uint8 *)&amp;_localip, (uint8 *)&amp;strM2MAPConfig.au8DHCPServerIP[0], 4);
    _submask = 0x00FFFFFF;
    _gateway = _localip;

    // WiFi led ON (rev A then rev B).
    m2m_periph_gpio_set_val(M2M_PERIPH_GPIO15, 0);
    m2m_periph_gpio_set_val(M2M_PERIPH_GPIO4, 0);

    return _status;
}